This invention relates broadly to the filling and sealing of multiwall valve bags. More particularly, it concerns valve bags having a polymer composition in the valve structure that enables the bag to be sealed using electromagnetic energy in the radio frequency range (RF energy).
The various methods that are presently used to seal valve bags include resistance heating, use of an adhesive, such as glue, or use of electromagnetic energy, such as ultrasonic heating. None of these methods are entirely satisfactory as a commercial technique for sealing valve bags. For example, in sealing the valve structure by resistance heating, the high heat required for softening the polymer composition in the valve structure will frequently scorch the paper in the bag before the temperature gets high enough to soften the polymer. The use of an adhesive in the valve structure of the bag can also be undesirable, in that it may contaminate the product inside the bag. Heat sealing in the ultrasonics frequency range is sometimes undesirable because it can cause the product in the bag to overheat.
The present invention overcomes the problems described above by providing a means and method for sealing a multiwall valve bag by using electromagnetic energy in the radio frequency (RF) range to heat a polymer composition that is fabricated into the valve structure of the bag. In this technique, the properties of the polymer composition allow it to respond specifically to the RF energy range, so that there is no deleterious effect on the paper or other parts of the bag structure during the sealing step.